The invention is directed to an electrophotographic printer means wherein charge images are generated on a photoconductor in the framework of an electrophotographic process in a sequence of process steps that sequence successively or, respectively, overlap one another, the charge images being generated via a character generator being developed in developer station, and being transferred onto a recording medium in a transfer printing station.
There is a significant difference between the acceptance of the copier result of electrophotographic copier devices and the printing result of printing equipment working on the principle of electrophotography by the operator: whereas the copier result in copier devices is measured against the original of the copy and the operator generally also accepts poor copies, this is not the case in electrophotographic printing equipment.
Electrophotographic printer means are generally employed in conjunction with EDP systems and the possibility of influencing the print quality is low or, respectively, the operator expects that the printer will deliver an optimum printing result under all conditions. Demands made of quality of the electrophotographic process that differ in height between printers and copier devices derive therefrom.
In order to satisfy this high demand with respect to the print quality in printers, it is necessary to minimize the tolerances in the electrophotographic process.
The quality of the commodities such as toner and developer or, respectively, the manufacturing quality of the photoconductor also have a significant influence on the print quality. The printer manufacturer has less influence on the quality of these materials during operation of the printer means.
In copier devices, it is known to regulate the units participating in the electrophotographic process to prescribed standard values via regulating means.
For instance, patent abstracts of Japan, Vol. 10, No. 288 (p-502) (2344), Sep. 30, 1986, and JP-A-61 105 578 disclose that the charging means for a photoconductive drum be controlled such for a defined time span during an after the turn-on phase that the fluctuations of the generated surface potential due to the turn-on event are compensated.
Patent Abstracts of Japan, Vol. 7, No. 101 (P-194) (1246), Apr. 28, 1983, JP-A-58 25 677 also disclose that the value of resistance of the paper web be acquired before the transfer printing station with the assistance of a multi-stage comparison means and that the corona discharge of the transfer corona in the transfer printing station be controlled step-by-step dependent thereon.
Patent Abstracts of Japan, Vol. 7, No. 184 (P-216) (1329), Aug. 13, 1983 and JP-A-58 86 562 disclose a regulating method for an electrophotographic copier means. The toner density and the residual charge on the surface of a photoconductor are thereby sensed with the assistance of a generated toner image of a standard image. The values acquired and calculated in this way are compared to prescribed standard values and a developer circuit, an illumination circuit, a toner delivery circuit and a developer sequence are controlled dependent thereon via a microcomputer circuit. Among other things, a reflection-type density measuring means and surface charge sensor are employed as sensors.
A standard original is imaged on the photoconductor with the known arrangement and the developer station is regulated dependent on the values of the standard original. What this means is that standard values of the electrophotographic process averaged over the standard original are acquired and different originals are copied with reference to these standard values proceeding on the basis of these standard values.
This has the disadvantage that an adaptation to different originals is not possible. Poor originals are developed as poor originals; a regulation of the standard values themselves dependent on the copying result is not provided.
U.S. Pat. No. 3,788,739 also discloses an electrophotographic means wherein a section in the printing region on a photoconductive drum is exposed with maximum illumination intensity and is then sensed with the assistance of a charge detector. The measured potential is then compared to a prescribed value. An adaptation of the values of potential in the charging, in the exposure, and in the transfer printing corona then ensues via a control means dependent on the measured potential.
Although the operating parameters critical for the image generating are also identified in electrophotographic printer and copier devices as disclosed, for example, by Japanese References JP-A-58 11 5453 and JP-A-58 221858, every operating parameter, however, is then compared prescribed, fixed manipulated variable and the manipulated variable for the process of image generating is defined therefrom.